• The Fractional-horsepower motors line up modified, by using D.C.,or A.C. circuits of any given power are called universal motors.
  • The universal motor is aimed at gaining marketable occurrences from sixty cycles to D.C. circuit with zero frequencies, where the voltage ranges from 250 Volt to 1.5 Volt.Though it must be noticed that a universal commercial motor might have a feebler series field and high armature conductors compared to a D.C. series of the motor which is corresponding to horsepower.Generally, it is factory-made with ratings ranging from 3/4 H.P, especially applicable for vacuum cleaners and industrialized sewing machines. Smaller sizes of ± H.P. are used in hand drills driven by electricity.

Similar to other series motors, the universal motor has the least speed without a load is considered as comprehensively high. However,gears of trains are constructed as the motor covering of some other universal motors that provideles least speed at extraordinary torque.

The application of motors as some commercial applications are such as electronic shavers, stitching machines, machines for offices, small handy hair dryers or vacuum cleaners. These appliances are openly burdened with the slight vulnerability of the motor.

Merits of a Universal motor:

  1. Extraordinary speed ranging from 3600 r.p.m. to almost 25000 r.p.m.
  2. Output in minor physical sizes for its application of portable tools.
  3. The elevation in torque at very low and transitional speeds just to carry an exceptional severe load.
  4. The different speed by the adaptable regulator is maintained by the line voltage or by the-recent pulse methods.


  1. The amplified facility of the prerequisite is only because of the use of the brushes and commutators. However, the lifespan of these components is restricted to a particular period.
  2. Comparatively,it has a greater level of noise at high speeds.
  3. It occurs medium to maximum radio and television intrusion due to the brush sparking.
  4. There is a necessity for carefully balancing things that help to escape vibration.
  5. The importance of the reduction of gearing of the portable tools must be taken care.

Fig. 21. Field cores of two pole universal motor.

The Universal motors are produced in two ways:

  1. Strenuous-rod, non-reimbursed type (small H.P. rating).
  2. Dispersed field reimbursed type (great H.P. rating).

The plastic-coated field configuration of a characteristically high field universal motor is represented in the Fig. 21.

The mechanism of a Universal Motor: there are motors which develop in a single direction torque irrespective of whether they act on the A.C. / D.C. supply. Thus the production of single directional torque takes place from when motor starts running on A.C. supply. To understand the phenomenon take a look at Fig. 22.

Well, this motor functions on similar principle when compared to a D.C. motor. Its principle involves the force amongst the core pole fluctuation, and current consisting the conductors of the body in spite of it being alternating or direct.

The Fig. 23 represents a particular torque with a universal motor of both for the A.C. and D.C. supply.

The ensuing methods may control the acceleration of any universal motor:

  1. Reactance method.
  2. Tapped-field method.
  3. Centrifugal mechanism.


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